One important factor in the transmission of certain diseases, most importantly HIV or AIDS, which can be transmitted through blood to blood contact, is the reuse of needles or syringes. Thus, a needle once used by a person infected with the AIDS virus or HIV is contaminated, and if the needle is then used by some other person, they will thereby become infected. This is particularly true of drug abusers, but may also be the case in other areas of syringe use.
One solution to the problem, in the form of a single-use syringe, has been disclosed in British patent application No. 8815355.6 published under serial No. GB-A-2220143A. The syringe disclosed is supplied in a fully depressed condition and, by virtue of a tapered locking ring surrounding a tapered portion of a piston, the piston may be withdrawn to fill the syringe. Inward pressure to dispense the contents disengages the locking ring from the piston, and therefore a second withdrawal is not possible.
However, desperate people may always try to overcome the above safety system. For example, they may attempt to push the piston and plunger back, either by inserting an elongate object through the nozzle opening or by forcing a fresh dose of injectant fluid into the syringe via the nozzle opening.
The present invention aims to provide a single-use syringe of a type which cannot easily be used a second time and therefore cannot contribute to the spread of diseases transmitted by contaminated blood or the like.